Bovine NK subsets in the afferent lymph and lymph nodes have distinct expression of naïve and activation-associated cell surface expressed molecules, and are differentially stimulated by BCG vaccination

Bovine natural killer (bNK) cells are heterogeneous cell populations defined by constitutive expression of the natural cytotoxicity receptor, NKp46 (CD335). Two major subsets of bNK cells, classified by differential expression of CD2, display divergent functions in innate immunity, and are hypothesised to contribute to adaptive immunity following vaccination. Here we characterised phenotypic variation of bNK cells within afferent lymph and lymph node (LN) tissues and between CD2⁺ and CD2^- bNK subsets, and report phenotypic changes induced by BCG vaccination. CD2^- bNK cells, which dominate in the afferent lymph and LN, displayed lower expression of the activation marker CD25 within the LN, with CD25⁺ cells being less than half as frequent as in afferent lymph. Furthermore, we found bNK cells had a lower expression of CD45RB, associated in cattle with naïve cell status, within LN compared to afferent lymph. Following BCG vaccination, bNK cells in afferent lymph draining the vaccination site showed increased CD2^-CD25⁺ frequencies and increased expression of CD25 on CD2⁺ bNK cells, although the frequency of these cells remained unchanged. In summary, we provide an overview of the phenotype of bNK cells within bovine lymphatic tissues, and provide an indication of how subsets may diverge following BCG vaccination.